Ferrari's Kimi Raikkonen set the quickest time in Thursday's opening free practice session for the Monaco Grand Prix.

The reigning world champion, seven points clear in this season's Drivers' Championship, posted a time of one minute 15.948secs around the 2.075-mile circuit.

Lewis Hamilton was second quickest, the McLaren Mercedes star ending the 90-minute session 0.268 seconds behind the Finn.

Hamilton had spent most of the session - which had to be red-flagged for 16 minutes after a manhole cover worked itself loose on the street circuit - at the top of the timesheets.

But he was forced to settle for second again as Ferrari - and Raikkonen in particular - signalled their intent.

Hamilton's team-mate Heikki Kovalainen was third quickest, exactly 0.3 seconds down, with Ferrari's Felipe Massa completing the top four.

They were followed by Williams' Nico Rosberg and Robert Kubica in his BMW Sauber, with Fernando Alonso - winner of the last two Monaco races - seventh for Renault, over 1.5 seconds down on Raikkonen.

Honda's Rubens Barrichello, Red Bull's Mark Webber and Force India's Giancarlo Fisichella - on the occasion of his 200th grands prix - completed the top 10.

Jenson Button was 12th for Honda, with David Coulthard 20th and last after failing to set a time - the Scot's Red Bull suffering a small fire early on.

BMW Sauber's Nick Heidfeld also suffered problems, slowing and pulling off track just before Casino Square, as did Jarno Trulli who buckled his left-rear wheel after clipping a barrier coming out of the tunnel.

The session was held under clear blue skies; however, rain is forecast throughout the weekend, with the greatest likelihood of a downpour coming on race day.

Monaco Grand Prix, Friday practice, session one:

01 K. Räikkönen Ferrari 1:15.948 26 laps
02 L. Hamilton McLaren 1:16.216 26 laps
03 H. Kovalainen McLaren 1:16.248 27 laps
04 F. Massa Ferrari 1:16.292 25 laps
05 N. Rosberg Williams 1:16.653 27 laps
06 R. Kubica BMW 1:16.653 27 laps
07 F. Alonso Renault 1:17.498 25 laps
08 R. Barrichello Honda 1:17.511 26 laps
09 M. Webber Red Bull 1:17.798 22 laps
10 G. Fisichella Force India F1 1:17.883 26 laps
11 T. Glock Toyota 1:17.942 26 laps
12 J. Button Honda 1:18.153 25 laps
13 S. Bourdais Scuderia Toro Rosso 1:18.245 30 laps
14 N. Heidfeld BMW 1:18.263 13 laps
15 K. Nakajima Williams 1:18.274 28 laps
16 J. Trulli Toyota 1:18.360 16 laps
17 A. Sutil Force India F1 1:18.360 25 laps
18 N. Piquet Jr. Renault 1:18.955 32 laps
19 S. Vettel Scuderia Toro Rosso 1:19.176 35 laps
20 D. Coulthard Red Bull no time 3 laps